Because of the common use of overhead mounted electrical devices such as lights and fans by the ordinary consumer, safety considerations must be incorporated in the design of such devices. Proper grounding of electrically conducting parts and components is essential for reducing the risk of electric shocks. In many designs, electrical conductivity for grounding the various parts is provided through direct metal-to-metal contact. This is exemplified by one design of an overhead electric-motor-driven fan having a hanger configuration where the downrod has a threaded end onto which the motor housing is screwed. The screw threads between the interconnecting parts provide the direct metal-to-metal contact.
Another example of providing grounding to an overhead electric device is shown in U.S. Pat. No. 4,810,207, issued Mar. 7, 1989, by the same inventors as herein. That application describes an apparatus for releasably, electrically and mechanically attaching an electric-motor-driven device to an overhead support. The electrical connections are made simultaneously as the unit is being mechanically mounted. To assure electrical grounding, a set screw is used as the primary conducting means between the downrod and the motor housing. The use of a set screw, however, tends to push the downrod off-center and skews the assembly. This often leads to manufactures utilizing two or more set screws at spaced positions around the downrod, which merely increases the complexity of this device and its installation.
Another consideration affecting the safety of such devices is that they must be mounted or hung securely to prevent them from falling from their overhead attachment. For motor-operated overhead devices such as fans, this safety aspect is especially complex. The device is not only subject to the static gravitational force of its own weight, but also to the dynamic load created during operation. Vibration often occurs with imbalance in the moving parts of the appliance, which can cause the device to become loosened from its mounting and fall. For example, one type of overhead fan utilizes a threaded end on a downrod from the overhanging support structure for mounting the device. A set screw is provided to bear upon the threads to prevent the relative movement of the connecting parts. The fan rotation is normally in the direction of the threads. Of course, in reverse rotation, the fan will then operate in a direction counter to the threading. If the set screw is loosened during reverse fan rotation, the housing can become unscrewed from the downrod and fall, causing injuries to people or damage to property. The loosened set screws may also lead to grounding interruption.
It would therefore be advantageous to have a means to positively secure an overhead electrical device in place and at the same time establish positive electrical grounding continuity. Further, it would be advantageous that such means be able to withstand anticipated imbalances and vibrations of a dynamic load and to resist the rotational forces of motor rotation, regardless of the direction of rotation. In addition, it would be of particular interest for the means to be such that simple mounting and demounting would be possible so as to permit quick and easy installation and maintenance.